1. Technical Field
This invention relates to a press-clamping (or crimping) structure of a press-clamping terminal (or crimp-type terminal) to an electric wire, the press-clamping terminal having a conductor press-clamping portion of a generally U-shaped cross-section including a bottom plate and a pair of conductor caulking pieces which are upwardly extended respectively from opposite (right and left) side edges of the bottom plate and are bent inwardly to embrace a conductor of the wire and caulk the conductor so that the conductor is firmly attached to an upper surface of the bottom plate. The invention also relates to a press-clamping terminal suited for achieving the above press-clamping structure.
2. Background Art
Generally, a press-clamping terminal has a conductor press-clamping portion of a generally U-shaped cross-section provided at a rear end portion thereof, and further has a sheath caulking piece provided at the rear side of this conductor press-clamping portion (see, for example, JP-2005-174896). The conductor press-clamping portion of the known press-clamping terminal has a pair of conductor press-clamping pieces (also called a barrel) formed in an upstanding manner respectively on opposite (right and left) side edges of a common bottom plate of the terminal, and the pair of conductor press-clamping pieces are bent inwardly to embrace the conductor to thereby caulk the conductor so that this conductor is firmly attached to an upper surface of the bottom plate.
Generally, copper wires are used in a wire harness which is installed within an automobile, and it is difficult to use aluminum wires which are inferior in properties (physical properties) such as electrical conductivity, strength and so on, and such aluminum wires have been hardly used. In recent years, however, there has been an increasing demand for the use of aluminum wires in view of a lightweight design of a vehicle, a low fuel consumption resulting therefrom and recyclability.
In the case of using an aluminum wire, it has now been found that when a known terminal is used as it is, problems are liable to arise because of the difference in physical properties between the aluminum wire and a copper wire. For example, a conductor of the aluminum wire which is made of aluminum or an aluminum alloy is lower (smaller) in strength than a copper conductor of the copper wire, and therefore when a conductor press-clamping portion is excessively press-clamped to the conductor of the aluminum wire, a problem is liable to arise that distal end portions 3c of conductor caulking pieces 3b bottom on a terminal bottom plate 3a (that is, bite into the conductor 10 to come into direct contact with the terminal bottom plate 3a or to come excessively close to the terminal bottom plate 3a) as shown in FIG. 5, thus lowering a fixing force. Furthermore, that portion of the terminal which presses the aluminum or aluminum alloy conductor of the aluminum wire against the terminal bottom plate 3a concentrates only on the distal ends of the conductor caulking pieces 3b, and therefore the region (indicated by arrows in FIG. 5) where a contract load is larger is narrowed, and therefore a contact conductivity is liable to be reduced.
The inventor of the present invention has studied and analyzed the structures in which the above problems are liable to arise, and has found that the above problems are liable to occur when the following dimensional tendency is encountered. This will now be described with reference to FIG. 5.
Namely, when the two conductor caulking pieces 3b are bent inwardly to embrace the conductor 10, using a lower die and an upper die of a caulking jig, first, the distal end portions 3c of the two conductor caulking pieces 3b, while rubbing against each other at their outer surfaces, are moved toward the terminal bottom plate 3a, and then are moved generally outwardly away from each other. It has been found that in this condition, when the distance Lw between two points P2 of the distal ends of the two conductor caulking pieces 3b closest to the terminal bottom plate 3a is smaller than a height Lh from the point P2 (that is, a point midway between the two points P2) to a point P1 of contact portions of the two conductor caulking pieces 3b closest to the terminal bottom plate 3a in a direction perpendicular to the terminal bottom plate 3a (that is, when the relation, Lh>Lw, is provided), the above problems are liable to occur.
It is thought that the cause for this is that when the relation, Lh>Lw, is obtained, the area where the conductor 10 is pressed against the terminal bottom plate 3a by the distal end portions 3c of the conductor caulking pieces 3b is reduced, so that the region where a contact load between the terminal bottom plate 3a and the conductor 10 is larger is narrowed. It is also thought that another cause is that since the area where the conductor 10 is pressed against the terminal bottom plate 3a by the distal end portions 3c of the conductor caulking pieces 3b is reduced, the distance Ls between the distal end portion 3c of the conductor caulking piece 3b and the terminal bottom plate 3a is reduced, so that the bottoming of the conductor caulking pieces 3b is liable to occur. Incidentally, it has also been found that even when the relation, Lh=Lw, is obtained, the above problems can not be solved.